The present invention relates to an arc welding electrode having a fine powder coating which swells upon immersion in water and forms a gelatinous coating upon use that serves as an insulation coating, a heat source, an arc enhancer, and a fluxing agent in underwater arc welding.
Arc welding encompasses a variety of methods for joining metals, all of which involve the use of an electric arc as a source of heat to melt and join metals. The arc is initiated and sustained between a workpiece and an electrode. The electrode is then moved along the joint to be welded. The function of the electrode is to conduct a supplied current and to sustain the electric arc between the electrode's tip and the workpiece. There are two types of electrodes: consumable and non-consumable. The consumable electrode is specially prepared so that it not only conducts current and sustains the arc, but it also melts and supplies filler metal to the weld site.
At present, underwater welding involves the use of coated, consumable electrodes of the straight polarity type similar to those used in surface welding. The electrode hard coating acts as a fluxing agent, which prevents, dissolves, or faciliates removal of oxides and other undesirable surface substances. By creating a reducing or non-oxidizing atmosphere enveloping the arc, the electrode hard coating prevents contamination of the metal by oxygen and nitrogen. Absent such a reducing atmosphere, the oxygen would readily combine with the metal causing porosity and oxidation of the weld. Reaction with nitrogen would cause brittleness, low ductility and possibly low strength and poor corrosion resistance. Electrode hard coatings also facilitate arcing by insulating the sides of the electrode so that the arc is concentrated to a confined area. In addition, the electrode hard coating serves as a thermal insulator in underwater welding, thereby concentrating heat at the electrode tip.
The electrode hard coatings reduce impurities such as oxides, sulphur and phosphorus which tend to impair the deposited weld, and aid in ionization and maintenance of the arc. Electrode hard coatings provide material, such as silicates, which forms a slag over the deposited weld. The slag retards heat transfer between the deposited weld and the surrounding water and allows the deposited weld to cool and solidify slowly. The slow cooling eliminates entrapment of gases within the weld, permits solid impurities to float to the surface and has an annealing effect on the deposited weld.
There are four types of electrode hard coatings in general use. These are iron powder coatings, cellulose coatings, mineral coatings and combinations of cellulose and mineral coatings. Conventional electrode hard coatings contain some or all of cellulose, limestone, fluorspar, rutile, titania, asbestos, iron powder, iron oxide, clay ferro-silicon, ferromanganese and sodium silicate.
Specifications for electrode hard coatings are issued by the American Welding Society and American Society for Testing and Materials. Suitable electrode hard coatings for use with the invention include American Welding Society AWS3, AWS4, AWS6 or AWS8 designation electrode hard coatings. Other electrode hard coatings can be used with maintenance electrodes, non ferrous electrodes and others which do not conform to published specifications.
When welding in air, the electrode hard coating provides a slag deposit which covers and protects the deposited weld. However, steam generation and thermal shock created in underwater welding can cause the slag formed by the electrode hard covering to pop off the weld. The resultant quenching and undesirable rapid cooling of the deposited weld may cause embrittlement of the deposited weld. Thus, if adequate protection from water is not provided, the strength and ductility of welds formed underwater typically are lower than that obtainable using above surface welding.
One object of the present invention is to provide an underwater welding electrode capable of producing underwater welds of greater strength and ductility than previously possible. Another object of the present invention is to provide an underwater welding electrode with improved thermal insulating characteristics which facilitates arcing and more efficiently retards heat loss. Yet another object of the present invention is to provide an underwater welding electrode with enhanced arcing capability which will allow longer and varying arc lengths, similar to those encountered in above water welding. Still another object of the present invention is to provide an underwater welding electrode which allows smoother, more efficient welding. Yet another object of the present invention is to provide a simple underwater welding electrode to allow the underwater use of conventional surface electrode holders with limited modification, enabling surface welders with minimum training in underwater welding to function suitably as welder/divers. Another object of the present invention is to provide a dry powder coating on magnetized electrodes and/or pieces to be welded which will form and release a gel which will flow to the weld arc, imparting to the weld formed greater strength and ductility than previously possible. A further object of the present is to provide an electrode for welding in flammable or explosion-prone atmospheres.